Hi Jeff, Thanks very much for your response. As you noted, I do not understand the Basemap global sinusoidal coordinate system. Does this statement not set up a global sinusoidal cartesian coordinate system centered at (lon = 0.0, lat = 0.0)?
m = Basemap(projection='sinu', resolution=None, lon_0=0.0, lat_0=0.0) If so, I would expect m(0.0, 0.0) to return (0.0, 0.0) and m(0.0, 0.0, inverse=True) to return (0.0, 0.0). Instead, I get: >>> m(0.0,0.0) (20015077.371199999, 10007538.6856) >>> m(0.0,0.0,inverse=True) (-176.20919036912957, -89.999999999808395) Sorry if I am being obtuse. Many thanks for your help. -Tim On Tue, May 2010, 04 at 04:01:21PM -0600, Jeff Whitaker wrote: > On 5/4/10 2:03 PM, Timothy W. Hilton wrote: > >Hello matplotlib users, > > > >I am having trouble understanding the coordinate transformations in > >Basemap and pyproj. I have gridded MODIS vegetation data, with upper > >left corner and lower right corner given in projection coordinates > >(meters). I want to contour the data with Basemap. The data are in a > >sinusoidal projection, but the coordinates do not correspond to what > >Basemap seems to expect. > > > >The code below illustrates the problem. Proj translates the upper > >left to lat/lon correctly (-92.327237416031437, 30.141972433747089), > >while Basemap does not. > > > >#-------- code -------- > >from mpl_toolkits.basemap import Basemap > >from mpl_toolkits.basemap import pyproj > > > >ulm = [-8895604.1573329996, 3335851.5589999999] #upper left, meters > >lrm = [-7783653.6376670003, 2223901.0393329998] #lower right, meters > > > >sinu = pyproj.Proj(proj='sinu', lon_0=0.0, x_0=0.0, y_0=0.0) > >m = Basemap(projection='sinu', resolution=None, lon_0=0.0) > > > >print "ULM: " + str(ulm) > >print "Proj: " + str(sinu(ulm[0], ulm[1], inverse=True)) > >print "Basemap: " + str(m(ulm[0], ulm[1], inverse=True)) > >#----- end code -------- > > > >This gives: > >ULM: [-8895604.1573329996, 3335851.5589999999] > >Proj: (-92.327237416031437, 30.141972433747089) > >Basemap: (-159.99950210056144, -59.99995206181125) > > > >I'm sure I'm missing something really simple, but I've read a lot of > >documentation and I'm not sure what. > > > >Many thanks for any help. > > > >Best, > >Tim > > Tim: Basemap is using pyproj under the hood, but only supports a > subset of possible proj4 projections. The basemap sinusoidal > projection is global - you can't specify a subregion of the globe. > I think that's where the discrepancy is coming from. I'm sure > there's a way to plot your MODIS data on a global sinusoidal > projection - but it will involve transforming the coordinates to the > Basemap global sinuosidal coordinate system. > > -Jeff > ------------------------------------------------------------------------------ _______________________________________________ Matplotlib-users mailing list Matplotlib-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-users
